The prior art is replete with methods and articles used to confine or store a wide variety of environmental contaminants ranging from completely capping, in-situ, contaminated sediments that are left in-place in underwater environments; terrestrial landfills wherein dredged or otherwise collected contaminated sediments are placed within an engineered disposal site surrounded with an impervious liner system and capped with an impervious material; and the use of a reactive mat and/or reactive backfill that surrounds the contaminated material. Examples of reactive mats are found in U.S. Pat. No. 6,284,681 B1 ('681) and published application US 2002/0151241 A1 ('241). The reactive mats described in these two publications include one or more layers of reactive material each surrounded by geotextiles that allow contaminated liquid to pass through the reactive mat for sorption or reaction of the contaminate with a reactive material contained between the geotextile layers, and in the case of the '241 published application, the mat may be deployed vertically.
One of the major problems encountered with the use of reactive mats for controlling or confining contaminated materials, or in controlling or preventing leaching of contaminants from sediments and preventing the contaminants from entering ground water supplies or from traversing through a lake or ocean soil interface into the lake or ocean, is in the ability to provide a transportable mat having a sufficient volume or thickness of reactive material so that the mat provides very long term protection without the necessity of periodic replacement. The reactive mats described in the '681 patent and in the '241 publication provide alternating layers of geotextile/reactive material/geotextile/reactive material since a sufficient thickness of reactive material cannot be provided in a single reactive material core layer without that reactive material being lost during transportation or installation.
This assignee's U.S. Pat. Nos. 5,237,945 ('945) and 5,389,166 ('166) describe the manufacture of a water barrier formed from a clay-fiber mat that may include, intermixed with a powdered or granular bentonite clay, a powdered or granular liquid-interacting material, e.g., a contaminant-reactant, or providing the contaminant-reactant as a separate layer in the water barrier product. The water barrier mat formed in accordance with the '945 and '166 patents is manufactured by laying down geosynthetic fibers and the water swellable clay, with or without the contaminant-reactant material, simultaneously. In this manner, a geosynthetic composite material can be manufactured wherein the geosynthetic fibers are surrounded by the water-swellable clay, with or without the contaminant-reactant material, in initially forming a relatively thick geotextile. Such a mat must be subsequently consolidated after the initial formation of the mixture of powdered or granular material and fibers in an attempt to secure the fibers in position surrounding the powdered or granular material. The following problems may be encountered with filled mats manufactured by simultaneously mixing individual fibers together with powdered or granular materials in accordance with this assignee's U.S. Pat. Nos. 5,237,945 and 5,389,166:
(1) Because interior fibers within the geotextile are not secured to adjacent fibers, particularly in thick mats, there would be lateral movement of powdered or granular material within the mat, particularly at the center of the mat thickness; (2) Any reactive materials that have a relatively high hardness, e.g., coke breeze, will prevent needle-punching as a means to consolidate the mats described in the '945 and '166 patents, since the hard materials will cause needle breakage and frequent replacement of worn needles; (3) Needle-punching as a means to consolidate the '945 and '166 mats is limited to relatively thin mats, e.g., less than 1 inch or 2.54 cm (25.4 mm), since fibers are too short to traverse the thickness of thicker mats for effective connection; and (4) Because of the shifting of fibers and powdered or granular material during manufacture of the '945 and '166 mats, the powdered or granular material will not be placed within the mat in a consistent quantity (weight per unit volume) and, therefore, will not provide consistent contaminant reaction, contaminant sorption, or contaminant neutralization per unit area. Another issue with the '945 and '166 mats is that when water swellable sodium bentonite clay is utilized, with or without the reactive material, when the sodium bentonite clay swells, the resulting swell pressure restricts the aqueous flow through the mat.